[Linaro-uefi,RFC/RFT] Drivers/Net/MarvellYukonDxe: remove redundant copy on RX path

Message ID 1472577986-7907-1-git-send-email-ard.biesheuvel@linaro.org
State New
Headers show

Commit Message

Ard Biesheuvel Aug. 30, 2016, 5:26 p.m.
The RX path in MarvellYukonDxe uses DMA buffers allocated via
EFI_PCI_IO_PROTOCOL::AllocateBuffer(), and copies the contents of each
into a temporary buffer, whose contents are copied yet another time before
arriving at the caller of EFI_SIMPLE_NETWORK_PROTOCOL::Receive()

This is inefficient for several reasons:
- the streaming bus master DMA operations used for RX do not require the
  use of buffers allocated via EFI_PCI_IO_PROTOCOL::AllocateBuffer(), which
  may return uncached memory on platforms with non-coherent DMA
- EFI_PCI_IO_PROTOCOL::AllocateBuffer() performs page based allocations,
  which means the UEFI memory map is modified for every packet received,
  now that the improper reuse of DMA buffers has been fixed.

So drop the call to EFI_PCI_IO_PROTOCOL::AllocateBuffer(), and instead,
perform a pool allocation whose ownership is transferred from the RX ring
to the RX linked list, which removes the need for a copy.

Also, since pool allocations decay to page based allocations for sizes
that equal or exceed EFI_PAGE_SIZE, reduce MAX_SUPPORTED_PACKET_SIZE to
the Ethernet default of 1500  bytes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

It builds, but does it run? I have no clue, since I don't own a Juno or
a Softiron 1000. Comments and testing appreciated. Thanks.

 Drivers/Net/MarvellYukonDxe/if_msk.c | 26 ++++++--------------
 Drivers/Net/MarvellYukonDxe/if_msk.h |  2 +-
 2 files changed, 9 insertions(+), 19 deletions(-)


Ard Biesheuvel Sept. 22, 2016, 7:27 a.m. | #1
On 21 September 2016 at 23:29, Daniil Egranov <daniil.egranov@arm.com> wrote:
> Hi Ard,
> It's not working on Juno correctly.
> On Juno, the AllocatePool() returns address of the buffer which according to
> the MMU translation is the same as a physical address so the address used
> for DMA should be the same as the buffer address . However, the DmaMap() in
> ArmDmaLib.c has a check for the cache alignment. The address allocated by
> AllocatePool() is not cache aligned so DmaMap() is reallocating the buffer
> with DmaAllocateBuffer() in uncached memory. At this point the buffer
> allocated by AllocatePool() and DMA buffer allocated by DmaAllocateBuffer()
> are pointing to two different physical memory addresses. That is keeping the
> AllocatePool() buffer with no data.

This is a Juno bug, not a driver bug. The PCI on Juno is DMA coherent,
which means it should not be using ArmDmaLib for PCI DMA. The result
is that the device writes into the shadow buffer using cached
accesses, while the CPU's view of the same memory is uncached, which
means that, when it copies back the data to the real buffer, it is
seeing stale data.

Could you try moving to DmaLibNull?


diff --git a/Drivers/Net/MarvellYukonDxe/if_msk.c b/Drivers/Net/MarvellYukonDxe/if_msk.c
index ecd716a66b55..d49c8e92a69a 100644
--- a/Drivers/Net/MarvellYukonDxe/if_msk.c
+++ b/Drivers/Net/MarvellYukonDxe/if_msk.c
@@ -595,7 +595,7 @@  msk_newbuf (
   rxd = &sc_if->msk_cdata.msk_rxdesc[idx];
-  Status = mPciIo->AllocateBuffer (mPciIo, AllocateAnyPages, EfiBootServicesData, EFI_SIZE_TO_PAGES (Length), &Buffer, 0);
+  Status = gBS->AllocatePool (EfiBootServicesData, Length, &Buffer);
   if (EFI_ERROR (Status)) {
     return Status;
@@ -603,8 +603,7 @@  msk_newbuf (
   Status = mPciIo->Map (mPciIo, EfiPciIoOperationBusMasterWrite, Buffer, &Length, &PhysAddr, &Mapping);
   if (EFI_ERROR (Status)) {
-    mPciIo->FreeBuffer (mPciIo, EFI_SIZE_TO_PAGES (Length), Buffer);
+    gBS->FreePool (Buffer);
     return Status;
@@ -1630,7 +1629,7 @@  msk_txrx_dma_free (
       mPciIo->Unmap (mPciIo, rxd->rx_m.DmaMapping);
       // Free Rx buffers as we own these
       if(rxd->rx_m.Buf != NULL) {
-        mPciIo->FreeBuffer (mPciIo, EFI_SIZE_TO_PAGES (rxd->rx_m.Length), rxd->rx_m.Buf);
+        gBS->FreePool (rxd->rx_m.Buf);
         rxd->rx_m.Buf = NULL;
       gBS->SetMem (&(rxd->rx_m), sizeof (MSK_DMA_BUF), 0);
@@ -1933,23 +1932,14 @@  msk_rxeof (
     if (!EFI_ERROR (Status)) {
       gBS->SetMem (m_link, sizeof (MSK_LINKED_SYSTEM_BUF), 0);
       m_link->Signature = RX_MBUF_SIGNATURE;
-      Status = gBS->AllocatePool (EfiBootServicesData,
-                                  len,
-                                  (VOID**) &m_link->SystemBuf.Buf);
-      if(!EFI_ERROR (Status)) {
-        gBS->CopyMem (m_link->SystemBuf.Buf, m.Buf, len);
-        m_link->SystemBuf.Length = len;
-        InsertTailList (&mSoftc->ReceiveQueueHead, &m_link->Link);
-      } else {
-        DEBUG ((EFI_D_NET, "Marvell Yukon: failed to allocate DMA buffer. Dropping Frame\n"));
-        gBS->FreePool (m_link);
-      }
+      m_link->SystemBuf.Buf = m.Buf;
+      m_link->SystemBuf.Length = len;
+      InsertTailList (&mSoftc->ReceiveQueueHead, &m_link->Link);
     } else {
       DEBUG ((EFI_D_NET, "Marvell Yukon: failed to allocate receive buffer link. Dropping Frame\n"));
+      gBS->FreePool (m.Buf);
-    mPciIo->FreeBuffer (mPciIo, EFI_SIZE_TO_PAGES (m.Length), m.Buf);
   } while (0);
   MSK_RX_INC (sc_if->msk_cdata.msk_rx_cons, MSK_RX_RING_CNT);
diff --git a/Drivers/Net/MarvellYukonDxe/if_msk.h b/Drivers/Net/MarvellYukonDxe/if_msk.h
index a5025a39ecf3..66513d3c54c1 100644
--- a/Drivers/Net/MarvellYukonDxe/if_msk.h
+++ b/Drivers/Net/MarvellYukonDxe/if_msk.h
@@ -15,7 +15,7 @@ 
 #include <Uefi.h>